1. Field of the Invention
The present invention relates to a method for producing a coupler based on fiber-fused connection.
2. Prior Art
Recently, with the increased spread of sophisticated communication systems, transmission systems based on optical fibers have been increasingly introduced for the connection of LANs and other networks to promote OA and FA.
In a LAN based on optical fibers, optical separators and couplers are more frequently used than before for distributing light signals to multiple terminals and for transmitting signals in the reverse direction.
The conventional optical separator/coupler mainly incorporates a coupler (star coupler) having multiple input terminals to serve as a key element of an optical data bus network. As this communication network enables a signal transmitted from any one terminal connected to the coupler to be distributed to the other terminals, its application becomes increasingly widened.
The coupler as described above is conventionally fabricated as follows. As shown in FIGS. 7 and 8, two optical fiber core lines (a) and (b) are closely placed together to bring their clads at the middle of their lengths in contact with each other; the contacted clads are heated to melt to form a fusion-connected section (c); jackets (d1), (d2), (d3) and (d4) are placed over both limbs of each of optical fiber core lines (a) and (b) being moved from their ends (a1), (b1), (a2) and (b2), respectively; the fusion-connected section (c) together with the four ends of jacket limbs close to it are placed in a protective case (e); a hardening resin (f) such as an epoxy resin is introduced into the cavity within the protective case (e) to fill the cavity; and, when the resin is hardened, a coupler integral with the optical fiber core lines is obtained.
Resilient fibers inserted longitudinally beneath the jackets (d1), (d2), (d3) and (d4) and over the periphery of optical fiber core lines (a) and (b) are represented by (g) in the figures.
However, with the conventional method for fabricating a coupler as described above, it is necessary, after a fused-connection is performed on optical fiber core lines to be coupled, to place tubular jackets over the limbs of the optical fiber core lines one after another while those lines have resilient fibers disposed around their peripheries. Therefore, fabrication based on the conventional method is poor in workability, produces too voluminous fusion-connected sections, and is high in cost.
Particularly when a coupler involving multiple, small-bore optical fiber core lines with correspondingly slender jackets is fabricated, the fabrication requires much labor and time, and often poses a problem in productivity. Moreover, a coupler produced by the conventional method, if it has to be sufficiently reinforced, becomes voluminous and expensive, while it becomes fragile when it is left small.
This invention was derived from an attempt to meet the above problems inherent to the conventional technique, and aims at providing a method for fabricating a fusion-connected coupler which enables simple, rapid production of a small, robust and inexpensive coupler in a highly productive manner.
To attain the above object, the method for fabricating a coupler according to this invention comprises the steps of placing a plurality of optical fiber cords in parallel, wherein each of the optical fiber cords comprises an optical fiber core line covered with a jacket with resilient fibers disposed longitudinally around the periphery of the core line beneath the jacket; making a cut on a specified point on the jacket of each optical fiber core line to divide the jacket into two limbs, and sliding the divided limbs of each jacket in opposite directions thereby to expose the middle section of the underlying optical fiber core line; bringing the exposed sections of optical core lines into contact with each other; heating the contacted sections to melt to form thereby a fusion-connected section; sliding back each jacket limb displaced outward close to the fusion-connected section; placing the fusion-connected section together with the cut ends of jacket limbs close to it in a protective case; introducing a hardening resin such as an epoxy resin into the cavity within the protective case to fill the cavity; and wherein, when the resin is hardened, the involved elements and their connection are integrated within the protective case.